The present invention relates to a cooling system for V-engines and particularly for outboard motors and the like employing high capacity thermostatic and pressure relief controlled systems.
Outboard motors are generally water cooled with the cooling water derived directly from and returned to the body of water through which the motor is operating. A suitable water pump is secured within the lower unit of the outboard motor and connected by an inlet water passageway to a cooling jacket system in the engine and exhaust housing and the like. The pump establishes a relatively high flow of water through the engine, with the output pressure and flow directly related to engine speed to provide the necessary cooling which prevents overheating and damaging of the outboard motor and the engine. However, optimum engine performance is dependent upon providing a more or less controlled cooling of the engine. Thus, generally at idle conditions the engine is preferably operated at significantly higher temperatures than at high speed or wide open throttle conditions to minimize smoking, missfiring, and erratic operation.
Most outboard motors are of a two-cycle construction with the fuel and air intake derived through a pressurized crankcase system. As a result, the heavier fractions of the fuel and oil tend to condense on the inside of the engine parts and cylinders, collecting in any low spots. This phenomenon is well known under the name of puddling and is further known to be the cause of highly erratic idling, with undesirable smoking and missfiring particularly during acceleration. If the engine block is operated at approximately or above 140.degree. F., puddling problems are significantly reduced, because the higher temperature minimizes condensation of the heavier fractions of fuel and oil. Although even higher temperatures might provide some improvement in engine operation, they develop excessively and unacceptable high temperature under the cowl of an outboard motor unit. At wide open throttle, the danger of puddling and misfiring is essentially nil and consequently the engine may operate with high efficiency at low temperatures.
Various cooling systems have been suggested for controlling the temperature and developing a compromise between a relatively high block temperature at idle and relatively low temperature at wide open throttle. On such compromise system employs a pump providing an output directly proportional to speed with a pressure relief valve which establishes a closed cooling system until such time as the pressure reaches a selected minimum value.
The water pump is also normally provided with a small bypass opening to permit complete draining of the system and also minimize the output flow and pressure at low RPM to insure that the pressure relief valve does not open until the desired higher speeds are obtained. At such higher speeds the small bypass opening has essentially no effect on the flow characteristic.
An auxilliary thermostatic valve unit may also be coupled to the system and releases at a selected temperature which will be developed under idle conditions when the pressure is insufficient to open the pressure relief valve and thereby permit cooling flow through the engine. The thermostatic valve thus opens to hold the engine at a maximum idle operating temperature which can be safely employed. The valves have generally been located at a low point in the engine near the discharge of the cooling water. The control valves are normally provided with suitable bypass openings to prevent trapping of air and permit complete filling of the cooling system with water upon starting. This is highly desirable as without some continuous flow localized boiling and steam pockets might develop within the cooling system. The bypass openings also permits draining of the cooling water from the engine upon stopping.
A particularly satisfactory high capacity thermostat-pressure relief controlled system is disclosed in pending U.S. application, Ser. No. 348,661 which was filed on Apr. 6, 1973 and entitled "MARINE ENGINE COOLING SYSTEM EMPLOYING A THERMOSTATIC VALVE AND PRESSURE RELIEF VALVE MEANS."
Although such systems are widely employed in both inline and V-shaped engines, the use of a common pressure release and thermostatic valve for V-shaped engines has not been found to provide optimum cooling characteristics. In V-shaped engines, the cooling water is divided into paralled passageways between the two cylinder banks. The inventor has noted a tendency in such systems to develop areas in one of the banks within which air is trapped and other areas in which water tended to stagnate with local boiling conditions. Although venting systems would appear to be the obvious solution, the inventor has found that in fact the problem remains. Although such systems are employed, they do not provide a desired optimum cooling characteristic.